Am I being completely stupid or is this tougher than it might appear. I have spent longer on this than I have on many 'very hard' but have come to a complete standstill. If someone tells me it's not that difficult I'll publish where I have got to and ask for a hint .. but am I alone?!

I've not used x-wing or swordfish before so I might be missing something, but I've even tried those without (apparently) any success.

I did get hung up on this one for a little while, Phil. Maybe you're stuck in the same place I was. My big break came when I realized that the "8" in the bottom center 3x3 box had to be in row 8 -- either in r8c4 or r8c5. That allowed me to complete r8c8, and things went more smoothly after that.

If that's not the right hint, maybe you should post your current position. dcb

You need to look at r8c8 more closely. I see {1, 2, 3, 4} in column 8 already. I see {6, 7} in row 8, and I see there's a "9" in the bottom right 3x3 box, at r7c9. So the only apparent possibilities at r8c8 are {5, 8} ... and you can rule out the "8" because it has to be in the bottom center 3x3 box (in row 8). So r8c8 = 5. dcb

Unusually for me I panicked and coded up all possibilities in all remaining cells (I usually tend to prefer just looking and seeing .. along the lines that you have explained). There were so many small digits floating around that I missed the simple deduction - serves me right! I was looking everywhere but r8 (I had the 58 in r8c8). I am left wondering whether there was another way forward or is this one of those crunch points that has only one esscape route?

I've done that, too -- writing in too many possibilities too soon, I mean, so that the important information is hard to see. That's what practice is for, I guess. I don't know if there was another way forward from that point, or not. That was the one I found.

I found this one quite straight forward in that I did not have to go beyond the simple solving methods. I did not have to look for any sets (naked or concealed). It took me 64 minutes; this was beause when I do a puzzle labelled "Hard"; I only spend a few minutes finding a few easy numbers; I then go straight into writing, in every empty cell, all the possible candidates. I know this is boring and time consuming, but, (if done carefully without making errors) it makes looking for sets and other patterns much easier.

Still at it on this one... I don't see how Philmac got the 2s and 3s in boxes 1,4, 5, and 6. I see the 8/1 twins in row 4, col 2&3, and mapped out the 2's and 3's.

000 510 000
109 002 305
560 003 012

000 005 046
456 238 001
790 641 008

830 100 029
627 000 103
900 320 000

Hint? Thx.

Hello Guest, From your stated position I note that you have overlooked the fact that in the 3 x 1 set of boxes 3/6/9; you have a 3 at r2 c7 and another 3 at r8 c9. Therefore the 3 required in box 6 either can go in r5 c8 or in r6 c8. However; there is already a 3 in row 5 at c5 therefore the missing 3 must go in r6 c8. Now look at the 5s in boxes 4/5/6 and you will get another "solve". These two items should get you going again Regards from Simon Templer

Hello again Guest, From your corrected position; write in all the candidates for every emply cell. You will find that r8 c8 has only one possible candidate - a 5 - then look at the other the 5s now contained in boxes 3/6/9 - you can now place another 5. You should be okay now. Regards from Simon Templer

> I have written in too many possibilities too soon - so that the
> important information is hard to see.

This is wise counsel.
When I first started, doing a candidate profile (called "tiny writing" in
a "Guardian" article) was the only way that I knew. I had not looked
up "sudoku" in any search engine at that time. I coded up a solver in
dBase for what I understood to be the methods in the Guardian article
- and then found that it did not solve all the puzzles put to it!! After I
became acquainted with the more complex solver rules and methods
I gave up on the dBase project and gradually have concentrated on
"manual" methods - attempting to avoid the "chore" of coding up the
candidate profiles!

So, yes, patience is a virtue. Doing the candidate profiles is much
easier if one has resolved a lot of cells first by simple methods. It
does complicate the page but makes setting the candidate profiles
easier if one first prepares the "Missing" profile for each row/column
and records that at the edge of the grid by the relevant row/column.

With this 14th Nov puzzle, I was impatient and set the candidate profiles
at probably too early a stage. I paid the price by having a very "messy"
page - two lines have seven entries in the "missing" profile and at
least four others had six. This leads to overly long profiles for the
individual cells (eg 46789 appeared for r1c7) and thus makes scanning
for patterns somewhat harder than it should be. The row actually
resolved to three pairs and so having 68 in place of 46789 did make
progress much easier once that state had been reached!

Perhaps the greatest difficulty is achieving a balance between time
and detail. If "Look and See" enables a cell to be resolved, it is
generally quicker than deriving all the profiles and, also, simplifies
any future derivations. On the other hand, poring over the grid for
twenty minutes and seeing nothing is not very encouraging or, indeed,
inspiring to progress - the time could perhaps be better spent on
deriving the profiles!

Does anyone have any hints as to WHEN in a puzzle to take the decision
to develop the profiles rather than to continue looking for the "simple"
patterns?

I find that applying a logical approach (eg checking everything for 1,
then everything for 2 etc) can take an inordinate time and then, during
that process, I find that attention to an "evident" pattern could have
shortened the timespan considerably. We all know that searching for
a swordfish or turbot will take time and so my question is really for
any guidance on time management.